Measurement of Interfacial Tension between Polymer Liquids : Pendant Drop, Improved Imbedded Fiber Retraction and Steady Shear Flow Methods

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After application of a large step shear strain, a polymer droplet in an immiscible polymer matrix takes rod-like and spheroidal shapes before returning to the spherical shape. Change in semi axes of those droplets is calculated based on the Cohen-Carriere theory and the extension of the theory by Okamoto et al. From comparison with experimental data, it has been found that retraction of semi axes is well described by the theory using a hydrodynamic factor for the droplet associated with the viscous resistance of the matrix. The excess shear stress for rod-like and spheroidal droplets is predicted based on the Doi-Ohta theory by evaluating the interface tensor from the semi axes calculated. The predicted excess shear stress for the deformed droplet is close to experimental data of a polymer blend with narrow distribution of droplet size after normalization per one droplet with the volume-averaged radius. The effects of polydispersity and interaction with adjacent droplets in the blend are suggested for the remaining difference between the prediction and the data.

Section: Introductionmentioning

confidence: 94%

Retraction of Rod-like and Spheroidal Droplets and Stress Relaxation after Step Shear Strain in Polymer Blends

Takahashi

Okamoto

2007

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“…1) Elmendorp and de Vos 2 ) used the spinning drop method and Elemans 3) et al used the breaking thread method. Recently, the imbedded fiber retraction (IFR) method was used [4][5][6] and other methods have been introduced which are using the shear oscillation test. [7][8][9][10] When the interfacial tension was measured, the dynamic modulus can be predicted by the emulsion model.…”

Section: Introductionmentioning

confidence: 99%

Interrelationship between Interfacial Tension and Rheological Properties of LDPE/PS Blends.

S.Yang

Nam

S.Kim

et al. 2002

The relationships between the interfacial tension and rheological properties in LDPE/PS blend system have been investigated. The block copolymer SEBS has been used as a compatibilizer. The interfacial tension was measured by the breaking thread method. Its value of LDPE/PS was 5.52dyne/cm and it is decreased rapidly with SEBS contents to 1wt% and then level off to a saturation value of 3.1dyne/cm. From the oscillatory shear deformation test, G' of the LDPE/PS blend increased with the LDPE contents at low frequencies due to the interfacial tension while G" showed similar behavior with that of pure LDPE and PS. The emulsion model considering the interfacial tension and droplet size in blends could predict the dynamic storage and loss modulus in reasonable range. Gramespacher and Meissner's emulsion model was used in this study. When the SEBS 1wt% was added to the LDPE/PS blend as a compatiblizer, there was a slight drop of storage modulus at low frequency ranges. As the SEBS contents increased over 3wt%, however, there was a dramatic increase of storage modulus. It was because of the saturation of the interfacial and micelle formation. As the SEBS content increased, the droplet size of LDPE decreased and the amount of micelle increased at the LDPE/PS interface.(PS) blends. Breaking thread method was used to measure the interfacial tension of blends. Also, the effects of compatibilizer on the morphology and rheological properties have been investigated. While many researches mentioned about the mechanical properties improvement due to the addition of copolymer as compatibilizer, relatively few reported about the rheologi ca l char ac ter isti cs. 1 3-15 ) Styrene-ethylenebutadiene-styrene block-co-polymer (SEBS) was used as a compatibilizer 16) , and an experimental study was conducted to investigate the effect of co-polymer concentration on the rheological properties of LDPE/PS blends. EXPERIMENTSMaterials LDPE, PS, and SEBS were used in this experiment. LDPE was from LG Chemical (Tg 107.43°C, MI 3.0 g/10min, density 0.920 g/cm 3 ), PS also from LG Chemical (Tg 97.11°C, MI 3.3 g/10min, density 1.05 g/cm 3 ), and SEBS was Kraton G block-co-polymer from Shell company (density 0.9 g/cm 3 , MI 65 g/10min, EB block 70%, Styrene block 30%). CompoundingPrior to mixing operation, LDPE and PS were dried over 24 hours at 80°C, and SEBS over 12 hours at 60°C in an air circulating oven before being compounded to prevent the hydrolytic degradation during processing. The blend compositions of LDPE/PS were 5/95, 10/90, 15/85, 20/80, and the effect of SEBS copolymer was studied with 20/80 LDPE/ PS blends. The copolymer compositions investigated were 1, 2, 3, 5, 7, 10wt% relative to the total weight of the blend.

“…と変化する．界面のエネルギーが界面積に比例することを考えれば，この形状変化は界面積の減少と対応する． 18,19) 配向角 θは，アフィン変形で与えられる角度に等しく，形状回復の間一定に保たれることを見出した． 18,19) マトリックスの粘度が比較的高く，観測しやすいように液滴のサイズを大きくしているため，回転緩和の時間が非常に長くなり，観測時間の間では θが一定であるように見えるのである． 18,19) ダンベル形状の出現に関して，当時は無限の長さの棒状界面に現れるRayleighの不安定性の波の一部が見えているものと思っていた． 19) ダンベル中央のくびれ部の包絡線がコサイン波で表されるので 18,19) 安心していた．しかし，棒状からダンベル状への比較的短い時間の間にこのRayleigh波が成長することはできないことを最近見出した． 20) ダンベル形状の出現は，有限の長さの棒状界面の両端に現れる球根状の end-pinchingがその原因であることを示唆した． 20) 伸長した長軸a の収縮に伴う界面積Sの減少の実験結果を Fig. 2に示す． 19) 方法を提案した． 17) また，この新しい方法が，ブレーキング・スレッド法(界面のRayleigh不安定性から界面張力を求める方法)と同等の実験結果が得られることを示した． 17) さらに Hayashiらは，この繊維収縮法をPIB/PDMSの系に適用し，標準的なペンダントドロップ法と同等の実験結果を得た． 22) 2.2.3 液滴の長軸・短軸の時間変化の予測収縮過程にある軸対称の液滴に働く回復力と粘性抵抗力のバランスは次式で表される． 23) ここで，tは時間，L (= 2a) 一方，HPC25 %/PDMS 20/80(wt/wt) ブレンドでは，フルオレセインをHPC25 % に微量加え，偏光顕微鏡で液滴サイズの分布を測定した．Pre-shear後のr V /r N の値は1.93で，液滴相のサイズ分布はかなり広い．分布がある場合でも，Fig. 6が液滴サイズによらない換算形であることを利用して，スケーリングが次のように行える．まず，単一液滴の∆ G(t,γ) が，r 0 によらないユニバーサルな関数Fを用いて次のように表せる． Fig.…”

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Study on Structure-Rheology Relationships in Multiphase Polymeric Systems

Takahashi

2007

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Structure-rheology relationships have been studied on polymer blends, block copolymers and polymer composites. The excess shear stress of polymer blends with droplet/matrix structure after application of a large step shear strain is predicted fairly well by the Doi-Ohta theory, when the interface tensor describing the anisotropy of the interface can be evaluated from observation of the deformed interface shape. The frequency dependence of storage G' and loss moduli G" of polymer blends with bicontinuous structure shows a power law behavior with exponent of 0.75 − 0.83. For diblock, triblock and starblock copolymers with lamellar, cylinder and gyroid structures, power law exponents for the frequency dependences of G' are found to be 1/2, 1/3 − 1/5 and 0, respectively. The power law exponent for G' is sensitive to the curved structure in cylinder-forming samples, while the exponent is always 1/2 in lamellar-forming samples. The structure-rheology relationships are investigated for composites in which ceramics particles are dispersed in polymer blends with bicontinuous structure. It has been found that particles enter exclusively into one phase in binary polymer blends, when flexible polymer chains in that phase adsorb onto those particles and better compatibility than other polymer phase is obtained. The dispersed state of particles in the polymer phase is correlated with G' behavior at low and intermediate frequencies.